Corrosion resistance of pneumatic valve type selection

in the corrosive medium under the condition of pneumatic valves, anti-corrosion chemical equipment is the key place, if not properly choose the metal materials chemical pneumatic valves, slightly careless, light damage to the equipment, or caused by accidents and even cause disaster. According to the statistics, the destruction of the chemical equipment about % is caused by corrosion, so in chemical equipment selection should first pay attention to the science of material selection. Usually there is a myth that stainless steel is 'a universal material', no matter what medium and environmental conditions with the stainless steel, this is not correct, is very dangerous. For some commonly used chemical media talk about the main points of the selection below:

, acid medium: as one of strong corrosive medium, sulfuric acid is an important industrial raw material is very versatile. Corrosion of different concentration and temperature of sulfuric acid on the material difference is bigger, the concentration in the % above, temperature less than ℃ concentrated sulfuric acid, carbon steel and cast iron has good corrosion resistance, but it is not suitable for high-speed flow of sulfuric acid, is not used as pump pneumatic valve materials; Ordinary stainless steel such as ( CrNi） 、（ CrNiMoTi） Also limited use in sulfuric acid medium. So transport of sulfuric acid pump pneumatic valve usually use high silicon cast iron ( Casting and machining is difficult) , high alloy stainless steel, Alloy) Manufacturing. Fluorine plastic has good acid resistance, the use of pneumatic valve fluorine-butterfly pump ( F) Is a kind of more economical choice. If too much pressure, temperature, the plastic of the pneumatic valve with hit points, can only choose is more expensive than its ceramic ball pneumatic valve.

, hydrochloric acid medium: most don't hydrochloric acid corrosion resistant metal materials ( Including all kinds of stainless steel materials) And high molybdenum silicon also can only be used for ℃, % the following hydrochloric acid. And metal materials contrary, the vast majority of non-metallic materials of hydrochloric acid have good corrosion resistance, so the lining rubber and plastic pump ( Such as polypropylene, fluorine plastic, etc. ) Is the best choice of transportation hydrochloride. But if such medium temperature exceeded ℃, or when the pressure is greater than kg, any plastic ( Including polypropylene, fluorine plastic even ptfe) Will not be able to do, and now there is no ideal pneumatic valve on the market, but can have a try now emerging ceramic ball pneumatic valve, the advantages of this pneumatic valve is self lubrication, torque force is small, not aging, service life is much longer than the average pneumatic valve, its shortcoming is that price is much higher than plastic air valve.

。 Nitric acid medium: general metal corrosion and damage, mostly in nitric acid was quickly is the most widely used nitric acid resistant stainless steel material, all on room temperature the concentration of nitric acid have good corrosion resistance, it is worth mentioning the molybdenum stainless steel ( Such as, L) For nitric acid corrosion resistance not only no better than ordinary stainless steel ( Such as, And sometimes not. For the high-temperature nitric acid, usually with titanium and titanium alloy materials.

。 Acetic acid medium, it is one of the strongest material corrosion in organic acids, ordinary steel in all concentration and temperature of severe corrosion of acetic acid, acetic acid proof material is stainless steel, stainless steel containing molybdenum can also apply to high temperature and dilute acetic acid steam. For high temperature and high concentration of acetic acid or contain other corrosive medium such as strict requirements, can choose high alloy stainless steel or fluorine plastic pump.

。 Alkali ( Sodium hydroxide) : steel is widely used in ℃ below, % concentration of sodium hydroxide solution, there are also many petrochemical plant in ℃, while % the following USES the ordinary steel, although the corrosion increases, but the economy better. Ordinary stainless steel for corrosion resistance of lye no significant advantages compared to cast iron, as long as the medium for allowing a small amount of iron added, stainless steel is not recommended. For high temperature and alkali liquor with titanium and titanium alloy or high alloy stainless steel.

。 Ammonia ( Ammonia hydroxide) : most of the metal and nonmetal in liquid ammonia and ammonia ( Ammonia hydroxide) The corrosion is very slight, only copper and copper alloy should not be used.

。 Chlorine ( Liquid chlorine) : most of the metal pneumatic valve resistance to corrosion of chlorine gas is very limited, especially chlorine water, including various alloy pneumatic valve, in this case, the four fluorine pneumatic valve is a very good choice, but in the production of chlor-alkali chemical factory will find: four fluorine pneumatic valve with a slightly long, torque force increase, four fluorine aging problem will be highlighted, in this case the leak is fatal. Consider using four fluorine lined ceramic ball core to replace the original ordinary lining four fluorine pneumatic valve, using ceramic self-lubrication and four fluorine corrosion resistance will be a perfect effect.

。 Brine ( The sea) : the ordinary steel in sodium chloride solution and sea water, salt water corrosion rate is not too high, the coating should be used in general protection; All kinds of stainless steel has a very low uniform corrosion rate, but may be localized corrosion caused by chloride ion, usually adopt stainless steel is better.

。 Alcohols, esters, ketones, ethers, common alcohol medium such as methanol, ethanol, ethylene glycol, propylene glycol, ketone medium such as acetone, butanone, there are all kinds of methyl esters medium, ethyl ester, ethers media such as methyl ether, ethyl ether, butyl ether, their basic no corrosive, commonly used materials are applicable, the specific selection should also according to the requirements of the dielectric properties and related make reasonable choice. In addition it is worth noting that the ketone, ester, ether has solubility to a variety of rubber, when choosing sealing material to avoid mistakes.